1. Field of the Invention
This invention relates to the making of hardmetal lamina by electric discharge machining (EDM), commonly known as "spark erosion", using a wire electrode. The invention also relates to a method of making a hard metal surface tool comprising the steps of producing a hardmetal lamina by a method as above, and securing the lamina to the surface of a mounting bolster shaped to receive the lamina.
2. Description of Prior Art
The word "hardmetal" is used in this specification to denote powdered carbides of the transition metals, notably tungsten, tantalum, titanium and niobium, cemented into solid masses by mixing with powdered metal of lower melting point such as cobalt or nickel and then compressing and sintering. Hardmetal is characterised by extreme hardness and is often used for components subject to heavy wear or abrasion.
A method of machining referred to as "Electrical Discharge Machining" is known as disclosed in an article in "Tooling & Production" March 1977 pages 46-48 in which an electrical discharge is used to cut a piece of material by producing local heating. The use of hardmetal in places where there is expected to be heavy wear or a brasion is also known.
With hardmetal there has always been a problem of machining. Creating the fairly thin, but often complex profiles of the pieces of hardmetal needed to cover the vulnerable areas of tools has proved almost impossible, as hardmetal is so brittle. Thus, to cover a tool, many small pieces of hardmetal had to be used, with the attendant problem of the attachment of these pieces, and also of preferential wear of the joins.